Project Summary Childhood tuberculosis (TB) has greater risk of morbidity and mortality than adult disease, yet diagnostic and prognostic tests discovered in adults are less accurate in children. There is a critical need for more sensitive diagnostic tests for childhood TB that do not need respiratory sample collection; for prognostic tests that are more specific in Bacille Calmette Guerin (BCG)-vaccinated children; and for improved tools to monitor treatment. Two novel approaches, host blood RNA signatures and the T cell Antigen-Specific Activation assay, target complementary aspects of the immune response and offer promise as diagnostic, prognostic and treatment-response biomarkers of childhood TB. A prognostic RNA signature of TB risk that also shows excellent diagnostic sensitivity and specificity for active TB, and response to treatment that mirrors disease progression, has been discovered in adults. Validation by qRT-PCR has been achieved; parsimonious 11-gene and 6-gene versions have been developed with identical performance; and the signature shows promising diagnostic sensitivity and specificity when applied to published pediatric microarray data. A host blood biomarker that measures activation of M.tb-specific T cells also yields excellent diagnostic performance. We validated and translated this T cell biomarker to a simplified whole blood assay suitable for pediatric use on basic flow cytometers widely available to HIV screening programs. We will evaluate performance of these two biomarkers for diagnosis and prognosis of pediatric TB disease and explore response to treatment. We will enroll a cohort of children with household exposure to an adult TB patient; evaluate them for TB disease by standardized investigation algorithm using a rigorous case definition; and collect blood for biomarker assays at baseline. Children without prevalent TB disease will be referred for preventive therapy and thereafter followed for incident TB disease for up to 3 years. Children diagnosed with TB disease will have blood sampled during curative treatment. We will evaluate diagnostic performance of these host blood biomarkers compared with Xpert MTB/RIF Ultra and prognostic performance compared with interferon-gamma release assay (IGRA); discover whether innate immune genetic variants are associated with biomarker expression; and project public health impact and cost-effectiveness of biomarker-targeted screening strategies for pediatric TB. A host blood biomarker that displays a characteristic response through the spectrum of pathogenesis of pediatric TB, increasing from M.tuberculosis infection through progression to disease and resolving during treatment, would be a major advance towards better diagnostic, prognostic and treatment monitoring tools for childhood TB.